1. Field of the Invention
The present invention generally relates to cooling structures and cooling methods for electronic equipment, and more particularly, to a cooling structure and a cooling method for electronic equipment which is composed of a plurality of electronic devices superposed on each other.
2. Description of the Related Art
A structure where plural electronic devices are superposed on each other in a rack is applied for electronic equipment such as telecommunication equipment. More specifically, plural plug-in units wherein electronic parts such as an integrated circuit (IC) or a large scale integration circuit (LSI) are mounted on a printed wiring board are received in a shelf. The plug-in unit is plugged in a back board provided in the shelf by a connector of the plug-in unit so that a single electronic device is formed.
In the above-mentioned electronic equipment, the temperature of an inside of the electronic equipment rises due to generation of heat of the electronic parts or others. Because of this, a forced air type of cooling means is applied in order to keep the temperature of the inside of the electronic equipment as a desirable temperature. More specifically, a fan having a high cooling ability is installed and operated into the electronic equipment so that air is forcibly taken in the electronic equipment from the outside and circulated inside of the electronic equipment. As a result of this, the electronic parts which generate heat are cooled and then the heat is discharged outside.
Conventionally, the operation of the fan, which forcibly cools the inside of the electronic equipment wherein plural electronic devices are superposed on each other in the rack, is determined based on an air flow whereby the electronic devices can be cooled so that the temperature in the electronic equipment is prevented from exceeding a temperature at which it is guaranteed that the electronic devices can be properly operated, namely an operation guarantee temperature, on the assumption that the greatest number of the plug-in units are installed in the shelf so that a calorific value generated when the greatest number of the electronic devices are installed in the rack, namely a maximum calorific value, is generated.
According to the above-discussed conventional forced air type cooling means, the fan is set up and always driven so that the air flow corresponding to the maximum calorific value is always generated regardless of the amount of the rack actually occupied by the electronic devices. Therefore, the fan always consumes the maximum amount of consumption electric power.
However, as a matter of fact, the greatest number of the plug-in units is not always installed in the shelf. Hence, there are a lot of cases wherein the calorific power generated by the electronic equipment does not reach to the maximum calorific power.
According to the conventional forced air type cooling means, even in this case, the fan is set up and always driven so that the air flow corresponding to the maximum calorific value is always generated so that the fan generates air flow larger than necessary. Therefore, in the conventional forced air type cooling means, there is waste of electric power.
Meanwhile, in other conventional art, a necessary number of temperature sensors are provided at proper parts in the electric equipment. By this sensor, the temperature of parts generating heat on the printed circuit board is always detected directly or indirectly. In addition, in this art, in order to make the temperature in the electronic equipment be equal to a setting temperature, a signal corresponding to a difference between the temperature in the electronic equipment and the setting temperature is output to a rotation control part.